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1.
黄铁矿是一种分布广泛的硫化物,但不同条件下形成的黄铁矿中微量元素的分配各具特点。本文通过对黄铁矿空间分布特征及其中多种微量元素分配特点的研究,提出黄铁矿晕的概念,讨论了其地质意义,对南北两矿带成因的同一性提供了新的信息,并提出矿体不同部位黄铁矿中Co/Ni比值的差异规律可作为判断矿体剥蚀深度的标志。  相似文献   

2.
Chemical and bacterial reduction and dissolution of Fe and Mn-oxide and the concomitant solubilisation of Co and Ni were studied in a surface horizon of a New-Caledonia Ferralsol. Chemical extractions showed that Mn and Co were in a large part associated in Mn-oxides. The main part of Ni was associated with goethite, but a very small fraction was also associated with Mn-oxides. Anaerobic reducing bacterial activity was responsible for Fe solubilisation at a smaller extent than for Mn solubilisation and consequently for associated metal release. Submicroscopic investigations revealed the presence of a Mn-oxide containing Co, Ni and Al, close to a lithiophorite–asbolane mixed-layers Mn-oxide, which can be considered as a main source of easily available metals in this soil. To cite this article: C. Quantin et al., C. R. Geoscience 334 (2002) 273–278.  相似文献   

3.
Sulphide mineralisation associated with rocks from the Palaeoproterozoic Olary Domain (OD) and overlying Neoproterozoic Adelaidean sequences has undergone a complex history of metamorphism and remobilisation. In this study, new trace element and sulphur isotopic analyses of pyrites from a large number of deposits and paragenetic generations are combined with an existing data set to build up a sequence of mineralising events linked to the tectonometamorphic evolution of the region. The typically high Co/Ni ratios (>10) indicate that early strata-bound pyrite precipitated from a volcanic-related fluid, which had fluctuating activities of the two metals during the early stages of the evolution of the Willyama basin. This period of mineralisation was followed by a diagenetic concentration of sulphide mineralisation at the horizon known as the Bimba Formation, which occurred as a result of the differing redox conditions between the upper and lower sequences in the Willyama Supergroup. During the Mesoproterozoic (1600 to 1500 Ma) Olarian Orogeny, metamorphic remobilisation of strata-bound pyrite resulted in an epigenetic signature; the trace element concentrations of this generation were controlled primarily by the proximity of mineralisation to the mafic intrusive bodies found throughout the terrane. Further reworking of existing sulphides during the Delamerian Orogeny and associated granitoid-intrusive rocks led to the formation of a new generation of epigenetic pyrite that occurs in quartz veins in the Adelaidean sequences and veins that crosscut Olarian fabrics in the Olary Domain. δ34S results range from 16‰ to 11‰, but most data fall between 2‰ and 4‰. This association is suggestive of an initial uniform deep-seated crustal reservoir of sulphur, which has been repeatedly tapped throughout the metallogenic history of the region. The isotopic outliers can be explained by the input of biogenic sulphur or sulphur derived from oxidised, possibly evaporitic, sediments, respectively. Previous workers have invoked the Kupferschiefer and the Zambian Copperbelt as analogues to mineralisation processes in the Olary Domain. This study shows that δ34S and trace element data are suggestive of some affinities with the aforementioned analogues, but a more likely link can be made between epigenetic remobilisation in the Olary region and the iron oxide copper gold (IOCG) style of mineralisation found at the nearby Olympic Dam deposit.  相似文献   

4.
Petrographic and EPMA studies reveal the presence of discrete grains of uraninite and pyrite are being reported for the first time in quartz-pebble conglomerates from western margin of Bonai granite pluton, Sundargarh district, Orissa. Uraninite grains (2–3 μ in size) are subrounded to muffin shaped which show variation in UO2 (63.86 to 71.73 wt %), ThO2 (5.48 to 6.42 wt %) and RE2O3 (1.57 to 2.23 wt %). Pegmatitic source of uraninite is revealed by comparing UO2, ThO2, PbO, CaO content and ratios of UO2/ThO2 and CaO/ThO2 in uraninites from pegmatite and other environments and areas. Subrounded to muffin shape of uraninite, their association with subrounded pyrite and heavies like zircon, tourmaline, chromite, monazite, magnetite and their comparable chemistry with well established quartzpebble conglomerates of India and world are indicative of their detrital origin. Pyrite, minor chalcopyrite and rare galena are observed as sulphide phases in conglomerate. Variable shapes of pyrite, their low Co (up to 0.16 wt %) and Ni contents (up to 0.09 wt %) and Co/Ni ratio less than 1.0 (mean= 0.63) favours sedimentary/diagenetic origin.  相似文献   

5.
Komatiite-hosted disseminated Ni sulphide deposits in the Agnew-Wiluna greenstone belt occur both above and below the olivine isograd that was imposed on the greenstone sequence during the M2 metamorphic/deformation event. Deposits in the northern and central part of the belt and that are located below the isograd (Mount Keith, Honeymoon Well and West Jordan) have complex sulphide mineralogy and strongly zoned sulphide assemblages. These range from least-altered assemblages of pentlandite-pyrrhotite-chalcopyrite±pyrite to altered assemblages of pentlandite±chalcopyrite, pentlandite-heazlewoodite (or millerite), heazlewoodite (or millerite), and rarely to heazlewoodite-native Ni. Deposits to the south and that are above of the olivine isograd (Six Mile, Goliath North) are dominated by less complex magmatic assemblages with a lower proportion of weakly altered pentlandite±chalcopyrite assemblages. More altered assemblages are uncommon in these deposits and occur as isolated patches around the periphery of the deposits. The sulphide zonation is reflected by whole-rock reductions in S, Cu, Fe and Zn, whereas Ni, Pt and Pd and, with some exceptions, Co are conservative. The leaching of S, Cu, Fe and Zn from sulphide assemblages and the whole rock was initiated by highly reduced conditions that were produced during low fluid/rock ratio serpentinization. Consumption of H2O resulted in Cl, a component of the fluid, being concentrated sufficiently to stabilise iowaite as part of lizardite-rich assemblages. Once the rate of olivine hydration reactions declined and during and after expansion and associated fracturing of the ultramafic sequence allowed higher fluid access, a more fluid-dominated environment formed and new carbonate-bearing fluid gained access to varying extents to the ultramafic rock sequence. This drove Cl from iowaite (to form pyroaurite) and caused the sulphide assemblages to be altered from the original magmatic assemblages and compositions to those stable at the prevailing fO2 and fS2 conditions. Mass transfer was made possible via metal chloride complexes and H2S with fluids driven by deformation associated with the M2 metamorphism. Disseminated deposits in higher metamorphic grade terrains where olivine was stable during peak metamorphism did not undergo the metasomatism seen in the deposits in areas of lower metamorphic grade. Some minor leaching of S, Fe and Cu occurred around the periphery of the deposits during early, pre-M2 peak metamorphism, but once olivine stability was reached the driving force for the series of leaching reactions was exhausted. The effect of this process on the original magmatic sulphides is to induce significant variability in texture, mineralogy and bulk composition and to markedly reduce the Fe and S contents of the sulphide fraction (in extreme cases to zero for both elements), and to reduce the volume of the sulphide fraction per unit of Ni. These changes impact unfavourably on Ni sulphide recoveries and metallurgical characteristics of these Ni ores.  相似文献   

6.
Analyses of pyrite, chalcopyrite and magnetite from the volcanic-hosted Big Cadia stratabound iron-copper deposit in Central Western New South Wales show considerable variation in the minor elements Mn, Ba, Ag, Pb, Zn, Cd, Se, Co and Ni. The preferential concentration of Co and Cd in pyrite, Zn and Ag in chalcopyrite and Mn in magnetite can be attributed to variations in activities of the ions in the hydrothermal fluid at the time of crystallisation of the mineral phases, or in cases such as the concentration of Co in pyrite, dependent on compatible electronic spin states between Co2+ and Fe2+. Trace element concentrations, especially Co and Ni contents and Co:Ni ratios in pyrite (average Co:Ni ratio=17.1) support a volcanic exhalative origin of mineralisation at Big Cadia. Differences in trace element composition such as higher Ni contents in pyrite in contrast with other volcanic-hosted ores may reflect the more basic character of volcanic rocks underlying the Big Cadia deposit.  相似文献   

7.
滇西南墨江金厂金镍矿床金、镍赋存状态及成矿过程探讨   总被引：5，自引：5，他引：0  
墨江金厂金镍矿床位于滇西南哀牢山造山带中段,是西南三江地区一个独特的金镍共生矿床。笔者通过野外地矿物主要为针镍矿、辉砷镍矿、锑硫镍矿、黄铁矿等。依据矿(化)脉切割关系、矿石结构构造及矿物共生组合,墨江金厂金镍矿床成岩-成矿期共发育4个世代黄铁矿。沉积变质期以草莓状黄铁矿和胶状黄铁矿为主,热液成矿期可划分为:早阶段石英-针镍矿-辉砷镍矿-锑硫镍矿-黄铁矿;主阶段石英-黄铁矿-毒砂-硫锑铜银矿-自然金;晚阶段方解石-石英-黄铁矿。对矿区赋金镍贯通性矿物黄铁矿进行详细的电子探针分析,结果显示4个世代黄铁矿微量元素有所差异。其中热液主阶段黄铁矿中含有Au、As、Sb、Pb、Zn、Cu、Co、Ni和Te,显示其流体成分复杂。不同阶段黄铁矿Ni含量不同,沉积变质期黄铁矿中Ni含量较低,为0.00%~0.82%,平均0.26%;热液早阶段黄铁矿中Ni含量最高,为0.43%~3.15%,平均1.38%;热液主阶段黄铁矿中Ni含量降低,为0.00%~0.99%,平均0.22%;热液晚阶段黄铁矿中Ni含量最低,为0.00%~0.09%,平均0.03%。研究结果表明墨江金厂金镍矿床中主要含金矿物和含镍矿物形成于热液期,含金矿物形成晚于含镍矿物。Ni在热液流体中的迁移能力与流体温度正相关,温度越高,Ni进入黄铁矿晶格的能力越强。基于上述金、镍成矿过程研究成果,并对比国内外热液镍矿床的地质-地球化学特征,推断墨江金厂金镍矿床是一个受岩浆热液改造的中-低温热液金镍矿床。  相似文献   

8.
Lead isotope study has been performed on massive sulphide deposits of Ossa-Morena and Aracena Belt (South Iberia). Results suggest the existence of at least two ancient hydrothermal events. The first one, Upper Brioverian in age (～600–570 Ma), gave birth to Maria-Luisa and Puebla de la Reina massive sulphide deposits; it thus confirms the existence of a Cadomian orogen in South Iberia. Isotopic compositions indicate a local contribution of mantle-derived material (Maria Luisa mine), confirming the presence of ancient oceanic crust in Aracena Belt. This mineralising event seems to extend till the Armorican Massif. The second episode, Eo-Hercynian in age (～400–350 Ma) has allowed genesis of massive sulphide deposits of la Nava Paredon and Aguas Blancas, and could be coeval with the emplacement of South-Iberian massive sulphide ore deposits in the neighbouring South-Portuguese Zone. A more continental crustal source for later ore deposits could explain the much more important metal accumulation in this zone. To cite this article: É. Marcoux et al., C. R. Geoscience 334 (2002) 259–265.  相似文献   

9.
The amphibole metapyroxenite intrusion from Mamb (Cameroon) consists of enstatite, diopside-augite, edenite, and traces of plagioclase, biotite and rutile. It contains notable amounts of sulphides (pyrrhotite, pentlandite, chalcopyrite, pyrite and Co-rich violarite). The sulphide phase segregated during magma crystallization as immiscible droplets (≤ 1 mm) included in growing ferromagnesian minerals or aggregated in the silicate crystal mush to form an interstitial phase. However, observed sulphide assemblages are likely to result from low-T (≤ 300 °C) re-equilibration of high-T monosulphide solid solutions, more particularly during the Pan-African metamorphic event. The Mamb amphibole pyroxenite intrusion is tentatively considered as a potential source for Ni and Co mineralization.  相似文献   

10.
The Black Butte copper deposits (formerly known as Sheep Creek) are a group of sediment hosted, laterally extensive Cu–(Co–Ag) deposits hosted in dolomitic shale of the mid-Proterozoic Newland Formation. Copper–cobalt mineralization occurs in zones of massive, laminated pyrite that were locally reworked and infiltrated by Cu-rich fluids during early diagenesis. Cobalt, along with substantial nickel and arsenic, mainly occurs as impurities within early, porous pyrite, or as minute grains of sulpharsenides (i.e., cobaltite, glaucodot, and/or alloclasite). Later thermal events remobilized the Co, Ni, and As to form intergrowths of siegenite (Co,Ni)3S4 and tennantite. The temperature of this later event is constrained by the mineralogical assemblage to have been relatively low, between 125 and 225 °C. Although many of the characteristics of SEDEX-type deposits are present at Black Butte (e.g., laterally extensive massive pyrite horizons, interbedded black shales, abundant barite and local phosphate horizons, and rifted continental margin setting), the lack of economic Pb and Zn mineralization in the main deposits, and the abundance of Cu with high Co, is more typical of sediment-hosted stratiform copper deposits. The Neihart Formation, a hematitic quartz sandstone resting below the base of the Belt Supergroup, may have been an important source bed for Cu–Co–Ni–Ag fluids. It is speculated that these fluids, ideal for forming Cu deposits, were expelled along growth faults near the margin of the Belt Basin and deposited metals on or just below the sea floor in a setting that is typical of SEDEX deposits. This unique mineral deposit model may have applications to other districts where Cu–Co-rich sulfides are deposited in an exhalative setting.  相似文献   

11.
白秧坪银铜多金属矿集区位于兰坪盆地北部。矿集区可分为东、西两个成矿带。赋矿地层主要为上三叠统三合洞组碳酸盐岩、第三系始新统保相寺组碎屑岩和下白垩统景星组碎屑岩。矿体主要以脉状、网脉状及透镜状形式产出。作者通过显微镜观察、电子探针和扫描分析等综合分析技术,确认白秧坪银铜多金属矿集区中矿物组成相当丰富,已鉴定出的矿物超过50种,既有大量硫化物、硫盐、氧化物、硫酸盐、碳酸盐,又有自然金属及金属互化物、卤化物等。除常见矿物为黄铁矿、毒砂、白铁矿、黄铜矿、方铅矿、闪锌矿、黝铜矿、砷黝铜矿、铜蓝、斑铜矿、辉铜矿、雌黄、菱铁矿、方解石、铁白云石、重晶石、天青石和石英外,作者还鉴定出一些银、钴、铋、镍、砷、锑的矿物,如自然铋、辉铋矿、辉银矿、辉砷钴矿、硫钴镍矿、硫铜铋矿、硫铋铜矿、辉砷镍矿、车轮矿、硫砷铜矿、单斜硫砷铅矿、灰硫砷铅矿等。矿石中矿物种类较多,组成较复杂,存在Co,Bi,Ni等元素的矿物,构成白秧坪银铜多金属矿集区的一大特色。在兰坪盆地白秧坪银铜多金属矿集区各矿段内,除了Cu、Pb、Zn构成工业矿体外,矿石中Ag、Co、Ni、Bi及As、Sb、Ba等元素的含量也相当高,可作为Cu-Pb-Zn-Ag-Co-Ni-Bi矿石来综合开发利用。白秧坪银铜多金属矿集区中Ag、Co、Ni、Bi等元素富集条件为低温、中低盐度,形成压力较小的浅成环境;成矿流体是一种富含CO2的Ca2+-Na+-SO24-Cl-类型、由大气降水演化而成的盆地热卤水。成矿物质主要来源于含有基性火山岩的兰坪盆地基底变质岩系。  相似文献   

12.

Six minor sulphide occurrences hosted by the Lower Devonian Buchan Group have been investigated. Sulphide minerals and associated phases are hosted by both dolostone and limestone lithologies along stylolitized bedding planes, cross‐cutting fractures, low angle minor faults and in cavities. Mineralization was closely associated with minor structures of inferred Tabberabberan age (Middle Devonian), which it appears to have post‐dated, but was largely strata‐bound in nature. The mineralogy of the occurrences is simple and characterized by the following generalized paragenesis which reflects the increasing oxidation state and pH of the mineralizing fluids: pyrite (pseudomorphous after marcasite)‐galena ± sphalerite ± pyrite‐dolomite ± barite‐calcite ± fluorite ± dolomite.

The sulphur isotope composition of sulphide minerals varies from ‐32.1 to +4.1‰, with iron and base metal sulphide minerals forming two distinct populations around ‐25‰ and 0‰, respectively. A single barite sample gives a sulphur isotope composition of +22.4‰, which is similar to that estimated for Early Devonian seawater. Fluid inclusions in fluorite and calcite homogenize at temperatures in the range 160 to 212° C and have average salinities of approximately 10 wt% NaCI eq. Sphalerite contains up to 1.81 wt% iron which correlates with colour, and up to 1.43 wt% cadmium. The Pb isotopic pattern of galena suggests a source region with U/Pb(= μ) lower than the crustal average, and a high Th/U.

A genetic hypothesis is proposed which involves the circulation of saline fluids through the Snowy River Volcanics, which directly underlie the Buchan Group, during or at some time after the Tabberabberan Orogeny. Although the Buchan occurrences show features characteristic of both Mississippi Valley‐type and stratiform ore deposits, they are most directly comparable to the epigenetic zones of Irish carbonate‐hosted base‐metal deposits. However, Pb‐Zn sulphide mineralization at Buchan appears to have been associated with minor compressional structures, suggesting that a simple correlation with the Irish deposits is not directly applicable.  相似文献   

13.
Tailings deposited over the Castanheira, a stream which flows through the old Ag–Pb–Zn Terramonte mine area, showed a great potential environmental risk due to sulphide weathering, facilitated by the tailings–water interaction. The high concentrations of Al, Fe, Pb and Zn in the tailings are associated with the exchangeable, reducible and sulphide fractions and suggest sphalerite and pyrite occurrences. Oxidation of pyrite is responsible for the low pH values (3.38–4.89) of the tailings. The water from the Castanheira stream is not suitable for human consumption due to high concentrations of SO4 2?, Mn, Al, Cd, Ni, and Pb. The lowest concentrations of metals and metalloids were detected in downstream stretches of the Castanheira. However, As, Fe and Zn in deeper sediments tend to increase downstream. Significant concentrations of trivalent forms of arsenic were detected in water samples. In downstream stretches of the Castanheira, some free ions (Fe2+, Mn2+ and Zn2+) also predominate and the water is saturated with ferrihydrite, goethite, hematite, lepidocrosite and magnetite.  相似文献   

14.
Stratiform quartz-sulphide lodes in Ingladhal occur in a typical Precambrian green-stone-belt environment comprising metabasalts, tuff, chert and cherty iron-sulphide formation. Unusually high cobalt contents of metavolcanics and of sulphide minerals in orebodies suggest a consanguinity between ores and rocks. 90% of total nickel, 70% of total cobalt but only 30% of total copper in rocks occur in silicate phases and thus indicate an early separation of copper from cobalt and nickel. Unusually high non-sulphide copper in barren bedded cherts implies availability of Cu-rich solution prior to their lithification. Pyrite in sediments, in volcanics, and in orebodies is characterized by a distinctive pattern of Co-Ni distribution in each case. Partitioning of Co and Ni between coexisting sulphide pairs is complex, but gross equilibrium is indicated. Very high trace metal content of orebody pyrite sharply contrasts with very low such values in pyrite from adjacent sediments and points to a higher temperature of formation of orebodies.  相似文献   

15.
刘仕玉  刘玉平  叶霖  王大鹏 《岩石学报》2021,37(4):1196-1212
滇东南马关都龙是一个以锡锌为主,共-伴生铟、铜、铅、钨、铁、银等多种元素的锡锌多金属超大型矿床。虽然前人从矿物学、矿床地球化学、年代学等不同角度开展了较多的研究,该矿床锡锌多金属矿化为燕山晚期岩浆热液活动的产物已是不争的事实,但关于该矿床是否存在热水沉积作用及其与锡锌多金属成矿作用的关系依然存在较大争议。本文选取都龙矿区广泛存在的黄铁矿作为主要研究对象,在矿相学基础上利用LA-ICPMS对不同阶段黄铁矿的微量元素组成开展了系统的研究。野外及显微鉴定结果表明,矿区存在四种类型(期次)的黄铁矿,即:鲕状黄铁矿Py1;穿切或交代Py1的细脉状黄铁矿Py2;与闪锌矿等硫化物共生的自形黄铁矿Py3;包裹早期黄铁矿或闪锌矿等硫化物的他形黄铁矿Py4。LA-ICPMS分析结果表明,该矿床黄铁矿中富集多种微量元素,其中Co、Ni、As、Ge等元素以类质同象的形式存在黄铁矿晶格中,而其余元素多以显微矿物包体形式赋存于黄铁矿中。上述四期黄铁矿微量元素组成存在较大差别,Py1相对富集Zn和As,而其余微量元素含量较低,Co与Ni含量较低,Co/Ni比值远低于1.00,其微量元素组成与典型沉积作用形成黄铁矿基本一致; Py2与Py1具有相似的微量元素组成特征,其Co/Ni比值接近Py1变化范围; Py3和Py4除富集Zn、As外,Mn、Co、Ni、Cu、Sb、Pb、Bi元素含量也相对较高,其Co/Ni比值相对较高,多大于1,与典型岩浆热液型黄铁矿微量元素组成相似,而与沉积型黄铁矿差异明显。结合各阶段黄铁矿产出地质特征,对比不同类型黄铁矿微量元素组成,本研究认为:Py1鲕状黄铁矿为热水沉积作用形成; Py2为Py1变质改造形成的细脉状黄铁矿,其微量元素继承了Py1; Py3为岩浆热液活动形成的自形黄铁矿; Py4为岩浆热液活动晚期形成的他形黄铁矿,Ag和Bi组成作为区分不同成因类型黄铁矿的化学指标的潜力。矿区早期沉积作用形成鲕状黄铁矿过程可能为后期成矿作用提供了部分硫源及少量Zn等成矿物质,海西-印支期区域变质改造作用对矿区成矿作用影响不大,而燕山晚期岩浆热液活动才是矿区锡多金属大规模成矿作用的主导因素。  相似文献   

16.
The Hemlo deposit, near Marathon, Ontario, is one of the largest gold deposits in North America. It is stratiform within Archean metamorphosed volcano-sedimentary rocks. The main ore zone is composed of pyritic, sericitic schist, and massive barite. This is the first report of stratiform barite in the Archean of North America, but other occurrences have since been found west of Hemlo. The mineralization is substantially enriched in Au, Mo, Sb, Hg, Tl and V and lacks carbonate. Because of metamorphism and deformation of the body its genesis is uncertain.87Sr86Sr of .7017 for barite from the deposit is similar to that of the sedimentary barite west of Hemlo and to initial ratios of contemporaneous volcanic rocks. At the base of the main ore zone, barite with δ34S of +8 to +12%. was deposited with ~0%. pyrite. Upward, both barite and pyrite get isotopically lighter, with minimum values for pyrite, to ?17.5%, in non-baritic schist forming the upper part of the ore zone. In drill section, Au grades correlate with the isotopic composition of pyrite. This, and the association of fractionated sulphide with sulphate, suggests that Au, pyrite and barite were deposited contemporaneously. The linked, asymmetric distributions of S minerals and isotopic distributions, which are continuous from section to section, and the isotopic similarity of the Hemlo and western barites are consistent with a syngenetic depositional model.Two sources for the S minerals are considered. In the first, exogenous sulphate from a restricted basin were partially reduced in a geothermal system to form 34S-depleted sulphide. In the second, the sulphate and sulphide are of magmatic-hydrothermal origin. Sulphate and fractionated sulphide are uncommon in Archean rocks, but one or both occur with unusual frequency in major Archean gold deposits. Hydrothermal fluids of moderately high ?O2, containing sulphate and permitting isotopic fractionation between oxidized and reduced S species, may have favoured the dissolution, transport and precipitation of Au.  相似文献   

17.
The Cu ore of Ifri is a chalcopyrite stockwork hosted by Cambrian formations and was until now interpreted as a syngenetic massive sulphide deposit. Textural studies highlight two generations of pyrite early (Py I) and late (Py II) with respect to the regional deformation. The chalcopyrite stockwork overprinted Py II, outlining the epigenetic nature of the Cu mineralization. Regarding the origin of Cu-depositing fluids, the presence in the stockwork paragenesis of an U, W, Sn association and preliminary Pb/Pb dating of a brannerite belonging to this association suggest a contribution of the Tichka granite. To cite this article: L. Barbanson et al., C. R. Geoscience 335 (2003).  相似文献   

18.
《Applied Geochemistry》1998,13(2):213-233
Porewater concentration profiles were determined for Fe, trace elements (As, Cd, Co, Cu, Mn, Ni, Pb, Zn), sulfide, SO4 and pH in two Canadian Shield lakes (Chevreuil and Clearwater). Profiles of pyrite, sedimentary trace elements associated with pyrite and AVS were also obtained at the same sites. Thermodynamic calculations are used, for the anoxic porewaters where sulfide was measured, to characterize diagenetic processes involving sulfide and trace elements and to illustrate the importance of sulfide, and possibly polysulfides and thiols, in binding trace elements. The ion activity products (IAP) of Fe sulfide agree with the solubility products (Ks) of greigite or mackinawite. For Co, Ni and Zn, IAP values are close to the KS values of their sulfide precipitates; for Cu and Pb, IAP/Ks indicate large oversaturations, which can be explained by the presence of other ligands (not measured) such as polysulfides (Cu) and thiols (Pb). Cobalt, Cu, Ni and Zn porewater profiles generally display a decrease in concentration with increasing ΣH2S, as expected for transition metals, whereas Cd, Pb and Zn show an increase (mobilisation). The results suggest that removal of trace elements from anoxic porewaters occurs by coprecipitation (As and Mn) with FeS(s) and/or adsorption (As and Mn) on FeS(s), and by formation of discrete solid sulfides (Cd, Cu, Ni, Pb, Zn and Co). Reactive Fe is extensively sulfidized (51–65%) in both lakes, mostly as pyrite, but also as AVS. Similarities between As, Co, Cu and Ni to Fe ratios in pyrite and their corresponding mean diffusive flux ratios suggest that pyrite is an important sink at depth for these trace elements. High molar ratios of trace elements to Fe in pyrite from Clearwater Lake correspond chronologically to the onset of smelting activities. AVS can be an important reservoir of reactive As, Cd and Ni and, to a lesser extent, of Co, Cu and Pb. Overall, the trace elements most extensively sulfidized were Ni, Cd and As (maximum of 100%, 81% and 49% of the reactive fraction, respectively), whereas Co, Cu, Mn, Pb and Zn were only moderately sulfidized (11–16%).  相似文献   

19.
The Pb isotopic composition of rocks is widely used to constrain the sources and mobility of melts and hydrothermal fluids in the Earth's crust. In many cases, the Pb isotopic composition appears to represent mixing of multiple Pb reservoirs. However, the nature, scale and mechanisms responsible for isotopic mixing are not well known. Additionally, the trace element composition of sulphide minerals are routinely used in ore deposit research, mineral exploration and environmental studies, though little is known about element mobility in sulphides during metamorphism and deformation. To investigate the mechanisms of trace element mobility in a deformed Witwatersrand pyrite(FeS_2), we have combined electron backscatter diffraction(EBSD) and atom probe microscopy(APM). The results indicate that the pyrite microstructural features record widely different Pb isotopic compositions, covering the entire range of previously published sulphide Pb compositions from the Witwatersrand basin. We show that entangled dislocations record enhanced Pb, Sb, Ni, Tl and Cu composition likely due to entrapment and short-circuit diffusion in dislocation cores. These dislocations preserve the Pb isotopic composition of the pyrite at the time of growth(~3 Ga) and show that dislocation intersections, likely to be common in deforming minerals, limit trace element mobility. In contrast, Pb, As, Ni, Co, Sb and Bi decorate a highangle grain boundary which formed soon after crystallisation by sub-grain rotation recrystallization.Pb isotopic composition within this boundary indicates the addition of externally-derived Pb and trace elements during greenschist metamorphism at ~2 Ga. Our results show that discrete Pb reservoirs are nanometric in scale, and illustrate that grain boundaries may remain open systems for trace element mobility over 1 billion years after their formation.  相似文献   

20.
Cement-based materials play an important role in multi-barrier concepts developed worldwide for the safe disposal of industrial and radioactive waste in underground repositories. In this study, synchrotron based-techniques (micro X-ray spectroscopy (XAS) and micro X-ray fluorescence (XRF)) were used to investigate Co and Ni uptake by Hardened Cement Paste (HCP) with the aim of improving our understanding of the immobilization process of heavy metals in cement at the molecular level. For Ni and Co, XRF mapping revealed a highly heterogeneous element distribution as far as the concentration is concerned. The XAS studies further showed that Ni(II) forms predominantly layered double hydroxide (LDH) phases. In contrast to Ni, Co was found to be present in the oxidation states II and III. Co(II) is predominately incorporated into newly formed Co(II) hydroxide-like phases (Co(OH)2), Co-LDH or Co-phyllosilicates, whereas Co(III) tends to be incorporated into a Co(III)O(OH)-like phase or a Co-phyllomanganate.  相似文献   

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